Lilmike's Cinema F-20 - Page 3

The LMS-R has a little too much motor, not a good fit if you're after a flat response.

I am nearly done with the F-24. While the result looks like a simple stretch of the F-20 fold, it is not. It was essentially a refold to get the details right.

It turns out that the MFW is power-limited above the horn tuning frequency in either cabinet. Only reason to go to a "bigger" driver is if you need more SPL due to power handling.

No extra wraps - just stretched it a foot taller, which messed everything up.....but I said I would, so I did. It just took me a little more work to get it right than I thought it would.

Here is a comparison. You give up a few dB and get a few Hz of extension.



I'll take the dBs personally. When comparing the two, I doubt anyone would notice the addition of 3 Hz of extension unless they were playing sine waves or posting their response plots on the interwebz, while a few dB of headroom is a big deal. Neither one will do the super low stuff all that well, the driver simply runs out of gas. It is only a single 15" driver.

Compared to HTIB, this might be a little bit more than "some" bass....

It should work, but personally, I'd avoid that driver orientation. Cone sag will become an issue. Fortunately, this is not that hard to do.

Seal the end and cut the mouth through the side. Set the cabinet on the rafters, and extend the mouth as needed to get into the room. This way the horn can rest across several rafters and there is no weight on the mouth section. The longer horn might lower the tune by 0.42 Hz too.

Shoot me a PM if you want details.

Of course, getting these into the attic might be an interesting process.....they are not small.

Mine weighs 148 pounds. I built it with the cheap imported "birch" 13-ply from Home Depot that I've been looking to get rid of for a while...what better place to put it than into a test mule that might not work out.... Arauco might be a bit lighter, true Baltic birch might be a bit heavier.

The sound? Simply put, it is a horn, and horns sound clean because distortion is lowered. They don't seem as loud as a result, but I can assure you, they are plenty loud. I've not listened to music with mains through it yet (not enough daylight....and no help to move it....) but it measures and sounds better than what I am listening to now.... Well, that and I know if I did get it inside, I'd wind up dragging my other sub out instead....and I have not painted this cabinet yet.

Compared to a dual opposed MFW in a sealed box? While a pair of 15s makes for a capable sub, I doubt you could get 21 Hz at 115 dB with 300 watts into one dual-opposed MFW cabinet at less than 10% THD. I ran out of amp at 114 dB and ~5% THD.....

The sub mounts against the cutout inside the back chamber. The cutout and chamber are sort of visible in the picture of the insides in Post #1. There is plenty of room, I can fit a Tempest X2 in there with room to spare. I use Hurricane nuts and allen screws to mount the driver. Since I've started properly installing hurricane nuts, I've not had problems.

Here's how I install hurricane nuts:
Drill the right size hole in the right places (with a backer board to avoid chipout),
slightly countersink the flange side (opposite the driver),
clean the hurricane nuts with acetone or brake cleaner,
start a hurricane nut in the hole,
apply PL to the shank with a bent wire,
drive it in place with a hammer,
repeat as necessary,
then chase the threads with a tap when the PL is dry.

Here is a pic with a few notes about what goes where.



Here's a view (sort of) looking inside the chamber through the baffle. Pardon the messy shop.

@ beastaudio

I have lots of diagrams, I'm still working on the text though.

It would actually help me improve the assembly instructions if I can work with someone that has not built a horn before. Would you be interested in reviewing the directions once I get them put together? I'd really appreciate your input.

Open call to all potential builders.

Basic cutting and assembly instructions will be posted at the bottom of post one in the next day or so - please review and comment if you think I can improve things. It is probably best to keep the comments and feedback to PMs to keep the thread cleaner.

I dunno. My dog went and hid while I was testing. What aspect are you worried about?

Really - this does not do that much below 20 Hz. It is not designed to, the driver is the limit here.

I certainly wouldn't worry too much about it.

My dog has an aversion to loud noises, (4th of July is not a fun time....) and she is a bigger klutz than I am, so she gets tangled in and trips over the cords and cables, which can really mess things up during testing. Best for everyone if she just hides....

If there is no boost in the wrong place, the NHT amp will be fine. It is only 80 watts, so it leaves about 6 dB on the table. I used a BASH 300 I had sitting around, it was about the right size. The BASH 300 is around $150, there are also some other options in the same price range, like the Apex Senior and the Dayton SA240. 300 watts into a 4-ohm load is all you need with the MFW driver.